1. Field of the Invention
The present invention relates to a system for managing files shared in a network.
2. Description of Prior Art
In many systems for managing files shared by a plurality of users in a network, when a user edits a shared file, other users can open the file for read-only or they cannot edit it. This processing is used to prevent inconsistency in information from occurring when a same portion in the file is edited at the same time. For example, if data contents that was stored previously by a user is overwritten with data contents stored thereafter by a different user, the former data contents is lost for the previous user. Also, many systems for managing shared files do not allow a file to be edited at the same time even for different portions in the file.
However, if a file is edited at the same time at different portions by a plurality of users, the edited data can be stored by any of the users irrespective of the location of the edited portion, and the above-mentioned problem is avoided. When a file has a smaller size, a probability that a same portion is edited at the same time would be higher. However, as the file size becomes larger, the probability becomes smaller. In addition, the necessity to edit different portions at the same time becomes higher for a file of a larger size. Then, many proposals are proposed for management on editing of shared files.
For example, many techniques are proposed to manage a file for each of partial areas therein. In a system described in Japanese Patent laid open Publication 10-55300/1998, a file is divided into portions, and management means keeps data for each portion in a management table recording access situation and a person who accesses the file portion. When a request for accessing a file is received, it is asked for the person to designate an access portion. If the access portion is not used, the access is permitted, and the management table is updated. Then, the file can be accessed at the same time at different portions, without destroying a file, and it can be referred to or updated. In a system described in Japanese Patent laid open Publication 6-295299/1994 for electronic editing for a document file, a plurality of operators edits the file for each page at the same time. The document file is divided into pages, and a parallel editing flag, a user management table and an access map area are provided for each page. Further, an object table is provided for managing data on an object to be edited for each operator registered in the user management table, and updated data are automatically exchanged between a master file and the data file. Thus, portions to be edited by the operators are assigned preliminarily, so that a danger to edit the same portion can be avoided. A system described in Japanese Patent laid open Publication 6-12310/1994 permits editing only for one person in the unit of partial portion in a file. A table for exclusive control stores exclusive management information for all the partial portions in a file to be edited, while a relational information table stores information that relational information on a partial portion is kept in the same file or in a different file. When an editor apparatus starts editing of a partial portion in a file, it is checked with reference to the exclusion management table whether editing is possible or not, and if the editing is possible, the exclusion management table is updated to show that it is under the exclusion management. Further, with reference to the relational information table, it is checked whether a relational portion to the partial portion is present or not, and if it is present, it is subjected to the exclusive control by updating the exclusion control table. When the editing is completed, the exclusive management table is recovered to the state at the start and the exclusive management is canceled. Thus, a file can be edited at different portions at the same time while keeping consistency of the data in the file, and the consistency can be kept between a partial portion to be changed for editing at the time and other portions not changed.
It was proposed to permit to access data by updating latest information, without minding inhibition control. In a system described in Japanese Patent laid open Publication 5-225028/1993, exclusive control is performed for simultaneous accesses to a file shared by a plurality of users and manages read from and write to the file by the users. It is decided at each predetermined time whether information referred to now is the latest information or not, and if the information is not the latest information, the latest information is read and displayed in a display device. Data which may be changed continuously is locked in order to prevent inconsistency in the data, but unlocked when a certain time elapses after the last time when the data is changed.
However, in the prior art systems for managing files shared in a network, a plurality of users can edit different portions in a file, but the systems cannot be used easily by users. For example, in the simultaneous file editing described in Japanese Patent laid open Publications 10-55300/1998 and 6-12310/1994, the system itself has editing right to the files. Therefore, even when there is no person who is editing a file, a person who wants to access the file has to designate an access portion for the file, and this makes the operation inconvenient. In the system described in Japanese Patent laid open Publications 6-295299/1994, exclusive control is adopted to permit editing for only a person in the unit of partial portion. Then, it cannot be used easily when editing portions for a plurality of editors are not determined preliminarily. In the system described in Japanese Patent laid open Publication 5-225028/1993, the latest information is updated each predetermined time, and this wastes the network resources.